In general, the present invention is directed to systems wherein it is desired to mix two liquids having greatly differing densities upon the interaction of the two liquids. In particular, the invention relates to an improved design for a mechanical stirrer for a pyrometallurgical system of the type described in the U.S. Pat. No. 3,861,660, issued Jan. 21, 1975 owned by the assignee of the present invention, and incorporated herein by reference.
Liquid-liquid systems having large differences in specific gravities (e.g., at least 0.5), as well as such systems in which each liquid has a high specific gravity (e.g., at least 3.0) present unusual mixing problems. Where the liquids are at very high temperatures (e.g., pyrometallurgical slags and mattes) an additional problem is the erosion of vessel walls caused by turbulence of the liquids adjacent those walls.
According to the present invention it has been realized that certain stirrer parameters are important in optimizing the desired results in pyrometallurigical systems in which (a) particulate solid-liquid contacting is required and (b) liquid-liquid contacting is required. The present invention is directed to the latter improvements and my contemporaneously filed U.S. Pat. application entitled "Pyrometallurgical System for Solid-Liquid Contacting" is directed to the former improvements.
In various pyrometallurgical operations, contact between two liquid phases is required to achieve rapid reaction rates. An example is the extraction of molybdenum by the contacting of an iron-rich matte and molybdenum-bearing slags. In such operations in general, and in the extraction of molybdenum in particular, there is typically a lower denser liquid (i.e., the matte) and an upper lighter liquid (i.e., the slag). In order to achieve the benefits concerning freezing of slag on the stirrer as described in the aforementioned U.S. Pat. No. 3,861,660, the stirrer blade assembly must be suspended in the slag (the upper liquid). Thus, the successful enhancement of reaction rates must be provided with the scope of this constraint on stirrer placement.
It is thus a principle object of the present invention to provide an improved stirrer for use in a pyrometallurgical system which will efficiently promote a high reaction rate between liquids of different densities while being supported in the upper liquid.
It is a further object to provide such a stirrer which will so enhance the reaction rate without substantially imparing the phase separation of the two liquids or causing excessive damage to the reactor'walls.